This invention relates to a high frequency plasma generation apparatus, and in particular to a high frequency plasma generation apparatus suitable to a reactive ion etching apparatus, an ion shower apparatus, a sputter apparatus, etc. for fabricating thin films or semiconductor devices.
Recently it has been studied to utilize a high frequency plasma generation apparatus in a reactive ion etching apparatus, an ion shower apparatus, a sputter apparatus, etc. for fabricating then films or semiconductor devices for which a fine patterning process is required.
Plasma generation apparatuses known at the present time are ion sources for ion beam working apparatuses, in which arc discharge is maintained by thermal electron emission from a filament and plasma is generated with a high frequency by a magnetic field produced by a solenoid coil, from which plasma ions are extracted. Working apparatuses using this kind of ion sources are explained e.g. in "A New Production Technique: Ion Milling" by D. Bollinger and R. Fink, Solid State Technology, November 1980.
When this kind of plasma generation apparatus works with a reactive gas, long time work is difficult for the reasons that the filament is consumed excessively, that some gases make the electrodes dirty, etc.
In order to remove these drawbacks, it is sufficient to realize a plasma generation apparatus using no filament. Microwave plasma generation apparatuses are an example of this type of plasma generation apparatus. This kind of apparatus is explained in detail e.g. in "Microwave Ion Source" (N. Sakudo, et al., Rev. Sci. Instrum., Vol. 48, No. 7, July, 1977). In these microwave plasma generation apparatuses, plasma is produced by microwave electric power and provides a high quality ion beam suitable in particular for working semiconductor devices. However, they have drawbacks in that the apparatus is too complicated and that it is difficult to enlarge the diameter of the beam.
Further, another example of plasma generation apparatuses having no filament, are high frequency plasma generation apparatuses which have been reported in "Radio Frequency Ion Source Development for Neutral Beam Application" (K. H. Leung et al., J. vac. Sci. Technol. A2(2), April-June, 1984) as ion sources for neutral particle injection devices, which additionally heat plasma for nuclear fusion.
In such a high frequency plasma generation apparatus a plasma production chamber is formed by sealing the upper end of the cylindrical side wall with a back plate, and a high frequency coil is disposed at its central portion inside the chamber. Further, a starter filament and a gas inlet are introduced therein through this back plate and a permanent magnet, which generates a multi-cusp magnetic field, is disposed on the peripheral portion of the cylindrical side wall. In this way, plasma is produced by high frequency discharge by means of the high frequency coil disposed in the plasma production chamber and it is confined in a vessel by the multi-cusp magnetic field.
However, by this construction, since the high frequency coil is inserted in a plasma having an electric conductivity, electrical breakdown is apt to be produced at its surface by the high frequency electric field applied to the high frequency coil. This electrical breakdown can be prevented to a certain extent by an electrical insulation coating on the surface of the high frequency coil. However, the life of the coating exposed to a reactive gas is short and further the coating on the surface of the high frequency coil gives rise to a new problem in that the interior of the plasma producing chamber is polluted by gas released by the coating material.